Overuse injuries commonly plague distance runners, as these athletes are exposed to high volume, intensity, and frequency of repetitive loading. The Achilles tendon experiences a significant amount of loading as it plays a critical role in energy storage and release during running. As a result, Achilles tendon injuries are one of the most common running-related musculoskeletal injuries.

Tendon pathology has been described to occur over a continuum, from early reactive stages (acute) to later stages of dysrepair and degeneration (chronic). Clinical treatments are most effective when they are tailored to match the stage of tendinopathy, as there is evidence that tendons at different stages of the pathology continuum may require different treatment approaches. Since external loading is a modifiable construct, understanding how tendon responds to cumulative loading, particularly in athletes at an elevated risk of developing overuse injuries, may improve tailored intervention delivery focused on load-based management.

Ultrasound tissue characterization (UTC) is an innovative imaging tool used to quantify tendon’s structural integrity and response to loading. UTC has been used to evaluate tendon response to both acute and cumulative load in athletic populations. However, to our knowledge, no previous study has tracked the response of the Achilles tendon to cumulative load over an entire competitive season, when athletes are required to manage both high volume and intensity of training amidst the addition of competition. The ability of UTC to detect changes in tendon structure that may be associated with or lead to tendinopathy may provide an opportunity for individualized preventative rehabilitation. Therefore, the purpose of this study was to evaluate the monthly changes in Achilles tendon structural integrity via UTC in response to cumulative loading across a four-month competitive cross-country season in collegiate distance runners.

What did you do and what did you find in this study?

Collegiate cross-country runners who volunteered to participate in the study were followed over the course of the competitive season (August – November). Monthly UTC ultrasound images were collected of the bilateral Achilles tendons of each participant. The UTC software uses advanced, validated algorithms to quantify the level of organization of the collagen fibers within the tendon, which are then classified into four categories:

Type 1 = Intact, highly organized tendon bundles (green)

Type 2 = Less organized tendon bundles (blue)

Type 3 = Mainly fibrillar tissue (disorganized) (red)

Type 4 = Poor quality tissue, degenerative matrix (black)

We found that over the course of the competitive cross-country season, the UTC ultrasound echo-pattern of the Achilles tendon improved in this cohort of collegiate cross country runners. In particular, there was an approximate ~10% shift from Type II to Type I echo-types across the four-month season. This suggests that in highly-trained distance runners, the Achilles tendon was resilient to a full competitive season of repetitive loading. Interestingly, our findings are similar to a recently published study examining changes in tendon structure during a five-month pre-season period in Australian football players. To our knowledge, ours is the first study to-date using UTC imaging technology to serially assess a group of distance runners during their competitive season.

How do these findings impact the public?

Our findings provide important insight into the response of the Achilles tendon to repetitive loading from running. This suggests that in highly-trained distance runners, the Achilles tendon was resilient to a full competitive season of repetitive loading. The use of UTC technology during a competitive season may aid clinicians in proactively managing tendon health in runners. Future studies may utilize UTC to examine associations between tendon structure and clinical outcomes (i.e. pain, strength, biomechanics, function), and the effect of cumulative load on tendon health.